This invention relates to circuits for receiving and converting the sound portion of conventional commercial television telecasts into signals suitable for introduction into the antenna terminals of conventional AM/FM radio receivers such as those typically installed in automobiles.
Television audio signal converters have heretofore been proposed, illustrative of which are those disclosed in U.S. Pat. No. 3,135,922 granted to Robert C. A. Eland on June 2, 1964 and U.S. 4,021,737 which was granted to Burdick S. Trask on May 3, 1977.
According to the former patent, a converter is provided which may be used in conjunction with a conventional television receiver whereby standard broadcast FM signals may be received on the conventional television channels of a television receiver.
According to the latter, in a conventional intercarrier type television receiver, advantage is taken of the fixed difference between the audio and video carrier frequencies of each channel by using an antenna tuned to a fixed frequency for sensing signals of that frequency radiated by the audio IF section of the TV set for each of the channels. The sensed signals are amplified prior to being demodulated and de-emphasized. The signals are then pre-emphasized in accordance with standard FM broadcast practice prior to being frequency modulated about a selected carrier frequency within the commercial FM band of 88-108 megahertz. The resulting FM signal is then transmitted by an antenna at a signal strength which is strong enough to allow for clear reception by an adjacent FM receiver within a high fidelity system and yet weak enough to comply with broadcasting regulations.
The apparatus of the former patent appears to provide for utilization of certain conventional TV circuitry to discretionarily provide not only the processing of the audio portion of TV signals, but also, optionally, a major portion of the processing of conventional FM signals, thereby eliminating the need for certain circuit components required if TV and FM circuits are made essentially independent.
The apparatus of the latter patent includes a radio-frequency receiver tuned to the frequency of the audio portion of the IF section of the TV set and thereby selects an audio information bearing signal which, with suitable processing is subsequently rebroadcast to be received by the conventional input circuits of a standard FM receiver.
Although the foregoing circuits provide for utilization of audio-bearing signals of one type with circuits of another type, there has nevertheless been a continuing need for simple and inexpensive circuits which provide for the reception of the audio-bearing portion of TV signals and their utilization within conventional FM receivers to provide FM audio sound output.
In contrast with the proposals of the foregoing patents, the circuits of the present invention are relatively simple and provide an easy-to-connect and inexpensive alternative for receiving the audio portion of conventional TV signals and processing that audio for introduction into the input stage of conventional FM stereo receivers.